Absent or shortened nasal bone length and the detection of Down Syndrome in second-trimester fetuses.

Objective: To estimate the accuracy of evaluating nasal bone length, expressed as multiples of the median (MoM), for the detection of Down syndrome in second- trimester fetuses.

Methods: Expected normal median nasal bone measurements were established for an initial cohort of women receiving fetal ultrasound examinations at 15-24 weeks of gestation. Nasal bone lengths were converted to MoM with adjustment for maternal race and ethnicity using whites as the referent group.